This week's element is rhodium, a hard, shiny silvery-white transition metal that is 1000 times scarcer than gold. Rhodium has the atomic symbol Rh and the atomic number 45.

Since there aren't any minerals that contain quantifiable amounts of rhodium, most of the world's rhodium is obtained as a by-product of mining for other, more common, precious metals such as palladium, copper, silver, platinum, and gold. Most rhodium comes from South Africa and most rhodium is used in North America and Europe as catalytic converters in automobiles. Of all the metals, only rhodium can reduce the damaging nitrogen oxide gases in automotive exhaust to gaseous nitrogen and oxygen.

Rhodium is more valuable than any other element on the planet due to its extreme rarity combined with the demand from the automotive industry. Thus, those who invest in rhodium can demand any price they wish for this metal. But it does have other uses, particularly in the jewelry industry, where rhodium plating gives platinum or gold jewelry ("white gold") its lovely gleaming white surface, and protects sterling silver jewelry from tarnishing.

Perhaps the most interesting bit of trivia that I can tell you about rhodium is that, instead of being given a gold or platinum disc, Paul McCartney was given a rhodium-plated disc in 1979 in recognition for being the all-time best selling singer-songwriter.

But that said, I think the most interesting character of rhodium is its peculiar ability to absorb oxygen from the atmosphere without becoming oxidized itself. How does it do this? When melted, rhodium captures oxygen and then releases oxygen when it solidifies.

Here's the Professor to tell us a little more about this extremely rare precious metal: